Elektronische Bauelemente

SEMP8965

Fast Ultra High-PSRR, Low Noise, Low-Dropout,

600 mA Micropower CMOS Linear Regulator

01-June-2002 Rev. A

Page 11 of 11

http://www.SeCoSGmbH.com/

Any changes of specification will not be informed individually.

POWER DISSIPATION AND THERMAL SHUTDOWN

Thermal overload results from excessive power dissipation that causes the IC junction temperature to increase beyond a safe operating level. The

SEMP8965 relies on dedicated thermal shutdown circuitry to limit its total power dissipation. An IC junction temperature TJ exceeding 165°C will

trigger the thermal shutdown logic, turning off the P-channel MOS pass transistor. The pass transistor turns on again after the junction cools off by

about 30°C. When continuous thermal overload conditions persist, this thermal shutdown action then results in a pulsed waveform at the output of

energy to dissipate to its ambient air. An IC junction with a low thermal resistance is preferred because it is relatively effective in dissipating its

thermal energy to its ambient, thus resulting in a relatively low and desirable junction temperature. The relationship between θJA and TJ is as

follows:

thermally overloading the SEMP8965, refrain from exceeding the absolute maximum junction temperature rating of 150°C under continuous

operating conditions. Overstressing the regulator with high loading currents and elevated input-to-output differential voltages can increase the IC

die temperature significantly.

FAULT DETECTION

In the event of the occurrence of various fault conditions that cause failure in the output voltage regulation, such as during thermal overload or

transistor, a large pull-up resistor (100kΩ typical) is required to provide the necessary output voltage and yet without compromising the overall

sustain good load and line regulation at the output. This occurs typically during near dropout when the input-to-output differential voltage is less

than 110mV for a load current of 200mA. The SEMP8965 detects near dropout conditions by comparing the differential voltage against a

predefined differential threshold that is always slightly above the dropout voltage. This differential threshold is dynamical in the sense that it not only

tracks the dropout voltage as the load current varies, but also scale linearly with the load current.

SHUTDOWN

circuits, including the bandgap reference, are turned off, thus reducing the supply current to typically 1nA. Such a low supply current makes the

FAST START-UP

Fast start-up time is important for overall system efficiency improvement. The SEMP8965 assures fast start-up speed when using the optional

noise bypass capacitor (CC). To shorten start-up time, the SEMP8965 internally supplies a 500µA current to charge up the capacitor until it reaches

about 90% of its final value.